There is an urgent need for an above knee (AK) amputee's ability to control above knee prosthesis, regardless of age or physical condition, e.g. second world war veterans and geriatrics. The demand exists for an active, volitionally controlled above knee prosthesis. Current prosthesis are passive devices that are awkward, and the amputee has little or no control.
The basic problem involved with existing limbs is that while unilateral AK amputees routinely "flex" the prosthesis limb while walking, bilateral amputees most often walk with one or both knees locked to provide stability. The use of passive locks makes sitting, at best, difficult.
Current knee units for a patient's use include a mechanical locking system located at the knee joint. The amputee must reach down and disengage the lock while braced against a suitable support and then lower himself into a sitting position. The difficulty is such that the amputee only unlocks the lock when sitting down, while unlocked knees would also be optimal for walking on a level surface. The limitations of the conventional knee system are further demonstrated by the amputee's inability to traverse even the smallest of grades.
Previous attempts to provide myoelectrically controlled prosthetic devices are described in U.S. Pat. No. 3,631,542 to Potter, U.S. Pat. No. 3,501,776 to Beeker et al., U.S. Pat. No. 4,623,354 to Childress et al. and U.S. Pat. No. 4,314,379 to Tanie et al.
Additionally, many patents are directed to hydraulic devices for control of prosthesis movement. Some of these patents are U.S. Pat. Nos. 3,799,159 to Scott, 3,670,341 to Webb et al., 4,065,815 to Sen-Jung, 4,051,558 to Vallotton, 3,995,324 to Burch, 3,871,032 to Karas, 3,800,333 to Friberg, 4,212,087 to Mortensen, 4,662,486 to Stenberg, 4,578,082 to Sen-Jung and 4,775,037 to Stenberg.